Posted
by
Soulskill
on Tuesday March 26, 2013 @07:12PM
from the spread-cat-pictures-far-and-wide dept.

judgecorp writes with news that Google is beginning tests on white space spectrum to deliver broadband internet access to rural communities in South Africa.
"White space has the advantage that low frequency signals can travel longer distances. The technology is well suited to provide low cost connectivity to rural communities with poor telecommunications infrastructure, and for expanding coverage of wireless broadband in densely populated urban areas. ... Ten schools in the Cape Town area will receive wireless broadband to test the technology. During the trial, we will attempt to show that broadband can be offered over white spaces without interfering with licensed spectrum holders. To prevent interference with other channels, the network uses Google’s spectrum database to determine white space availability."

Most digital people seem to think that all frequencies act the same, or in this case, lower frequencies travel farther than higher frequencies.

Some even seem to think that Bandwidth is infinite.

This project smacks of BPL, (Broadband over Power Line) who's promoters seemed to think that you could impress Radio signals onto Power lines without interference to other services, and other services would not interfere with BPL..

The lowest Television channels, in the VHF portion of the band, are known as the "magic" band by Amateur radio operators, because the frequencies some times act like much lower frequencies, with long distance propagation, and some times like higher frequencies, with strictly line of sight distances. And there is noise also. The old school TV stations used a lot of power for a reason. Get that signal to noise ration as high as possible. And a meteor burst noise is going to disrupt digital immensely, and they happen all the time.

What ever could go wrong? There is a reason why those Gigahertz frequencies in use work for wireless. They are much more quiet, they specifically have much shorter range, which keeps everyone from interfering with everyone else, and the bandwidth is inherently higher at those higher frequencies. Look up Shannon's limit, and spare me the phase modulation infinite bandwidth bs, because the bandwidth become infinite - but the power need is also infinite. This is probably a Government Grant make some money for failing trick.

i'm pretty sure BPL was only limited because of transformers being in the way

BPL works fine for LAN within a home or business

also/quote>
What the issues with BPL were was that running the signals along the power lines acted as an antenna. Not a good antenna, but an antenna none the less.

The digital signal is a radio frequency wavelength signal, So it can escape from the line. Other signals can get into the line, also.

Hams regularly communicate around the world on HF with microwatts of power.

In tests, a one watt signal into a loaded whip at around 27 MegaHertz would shut adow all BPL for blocks around, imagine Ham radio operators who typically transmit at 100 Watts or more. and the BPL interfered with licensed services even though they used notch filters to keep the digital signals away from those services. I believe th eproblem was intermod, with two signals mixing to create a third, something else digital engineers often don't know.

It was basically a bad idea championed by people who didn't understand RF.

This project smacks of BPL, (Broadband over Power Line) who's promoters seemed to think that you could impress Radio signals onto Power lines without interference to other services, and other services would not interfere with BPL..

BPL tried to use a bunch of frequencies modulated over the power line. Of course, BPL proponents never considered that power lines were excellent antennas. That resulted in interference to the airwaves. This is a problem as power lines are NOT shielded.

They did not say they are using VHF low. They are most likely using VHF HI (>175 MHZ), or UHF frequencies between 400-700MHZ. These frequencies are in a "sweet spot", traveling much better than > 2GHZ signals and don't get hammered by Sporadic E, Meteor scatter or other weird propagation effects as much as lower frequencies.

Although from TFA, the hop they are doing is 6.2 miles. With decent towers and highly directional antennas on both ends, 2.4ghz could work.

If they are setting up communications transmitters in a foreign country, shouldn't Google be asking that country's national telecommunications administration which channels are clear to use and which are not? It probably never occurred to Google that every country in the world has its own version of the U.S. FCC, and for the same reasons that the FCC exists, that is to regulate such things as frequency allocations, exact channel assignments, transmitter powers, emission bandwidths, etc etc. Many countries

Here's a crazy question... Are the lower (white-space) frequencies really worth all the efforts? We're talking about UHF TV frequencies here, which generally only go up to 60 miles, really only slightly beyond line-of-sight (VHF can do quite a bit better). Outside of heavily wooded forests and dense urban cities, how much benefit are they getting out of these frequencies, versus needing to site their WiFi antennas better (ie. higher up), or having twice as many base stations repeating the signal?

Here's a crazy question... Are the lower (white-space) frequencies really worth all the efforts? We're talking about UHF TV frequencies here, which generally only go up to 60 miles, really only slightly beyond line-of-sight (VHF can do quite a bit better). Outside of heavily wooded forests and dense urban cities, how much benefit are they getting out of these frequencies, versus needing to site their WiFi antennas better (ie. higher up), or having twice as many base stations repeating the signal?

Is the benefit of slightly better range with the lower frequencies really worth buying custom equipment, rather than commodity $35 off-the-shelf APs? Neither the stories on Google or Microsoft's efforts with this tech actually say a non-trivial amount about the tech.

From what I've read, the primary advantage of using white space (802.22) is provisioning sparsely populated areas without building expensive point to point infrastructure. I have high hopes for the technology(ies). My only available 'net connectivity is via satellite (blech!), with its high latency, low throughput, punishing data caps, and unreasonable expense.